Combined cycle plant

ABSTRACT

In a combined cycle plant that combines a conventional thermal power plant and a gas turbine plant, there is provided a dump system  1  that connects a main steam pipe  60  with the condenser  25  and dumps the steam generated by the boiler  10  into the condenser  25 , bypassing the steam turbine; and HRSG HP turbine bypass system  2  and HRSG LP turbine bypass system  3  which connect the HP pipe  70  and LP pipe  71  of the heat recovery steam generator, respectively.

BACKGROUND OF THE INVENTION

The present invention relates to a combined cycle plant that combines aconventional thermal power plant and a gas turbine plant.

In a well-known combined cycle plant combining a conventional thermalpower plant comprising a boiler, steam turbine, condenser, etc. and agas turbine plant comprising a gas turbine and heat recovery steamgenerator, the steam generated by the boiler of the conventional thermalpower plant and the steam generated by the heat recovery steam generatorof the gas turbine plant are put together to drive the steam turbine.

A prior art relating to this type of power plant is disclosed, forexample, in the Japanese Laid-open Patent Publication No. 2000-220412.

SUMMARY OF THE INVENTION

A power plant is equipped with a system for dumping the steam generatedby the boiler into the condenser at the time of start, stop and loadrejection. Since the prior art mentioned above relates to a power plantthat combines a conventional thermal power plant and a gas turbine plantand so the plant is equipped with two steam generators, i.e. boiler andheat recovery steam generator, it is necessary to install two dumpsystems for dumping the generated steam into the condenser.Consequently, the system layout becomes complicated and multiple inletports need to be installed on the condenser.

The present invention provides a means for constructing a dump systemfor dumping the generated steam into the condenser without increasingthe number of inlet ports on the condenser of an existing plant.

A combined cycle plant according to the present invention is equippedwith a dump system that connects the boiler pipe with the condenser anddumps the steam generated by the boiler into the condenser, bypassingthe steam turbine, and a pipe that connects the heat recovery steamgenerator pipe with the dump system into the condenser.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of the combined cycle plant according tothe embodiment 1 of the invention;

FIG. 2 is a schematic diagram of the combined cycle plant according tothe embodiment 2 of the invention;

FIG. 3 is a schematic diagram of the combined cycle plant according tothe embodiment 3 of the invention;

FIG. 4 is a schematic diagram of the combined cycle plant according tothe embodiment 4 of the invention;

FIG. 5 is a schematic diagram of the combined cycle plant according tothe embodiment 5 of the invention; and

FIG. 6 is a schematic diagram of the combined cycle plant according tothe embodiment 6 of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention are described hereunder, usingFIG. 1 to FIG. 6.

<Embodiment 1>

A preferred embodiment of a combined cycle plant according to thepresent invention is described hereunder, using FIG. 1.

The power plant is equipped mainly with two plants: a conventionalthermal power plant comprising a boiler 10, a boiler pipe including amain steam pipe 60, cold reheat pipe 61 and hot reheat pipe 62,high-pressure (HP), intermediate-pressure (IP) and low-pressure (LP)turbines 21,22 and 23, respectively, a condenser 25, and a condensatewater/feedwater system; and a gas turbine plant comprising a gas turbine40, a heat recovery steam generator 50 that recovers heat from theexhaust of the gas turbine 40, and a heat recovery steam generator pipeincluding a HP pipe 70 and LP pipe 71.

In FIG. 1, feedwater supplied to the boiler 10 is heated by aneconomizer 12 and steam is generated by an evaporator 13. The generatedsteam, while being superheated through a primary superheater 14 and asecondary superheater 15, is directed as superheated steam into the HPturbine 21 through the main steam pipe 60 connecting the evaporator 13with the HP turbine 21.

On the other hand, the steam generated by the heat recovery steamgenerator 50 is joined into the main steam pipe 60 through the HP pipe70 connecting a HP drum 51 with the main steam pipe 60 and also directedas superheated steam into the HP turbine 21.

After having driven the HP turbine 21, the steam flows through the coldreheat pipe 61 and is directed to a reheater 11 of the boiler 10. Thesteam superheated by the reheater 11 is supplied to the IP turbine 22through the hot reheat pipe 62. On the other hand, the steam generatedby the heat recovery steam generator 50 is joined into the hot reheatpipe 62 through the LP pipe 71 connecting the LP drum 52 with the hotreheat pipe 62 and also directed as superheated steam into the IPturbine 22.

After having driven the IP turbine 22, the steam is led into the LPturbine 23 through a crossover pipe 63. The steam, after having driventhe LP turbine 23, is then led into the condenser 25 and turns tocondensate water.

The condensate water condensed by the condenser 25 is then pressurizedby a condensate pump 30 and heated by a gland steam condenser 31, andthen branched into the condensate for the conventional thermal powerplant and the feedwater for the heat recovery steam generator 50 of thegas turbine plant.

A condensate pipe 65 connecting the condenser 25 with a deaerator 34 isinstalled in the condensate water system of the conventional thermalpower plant. The condensate water in the conventional thermal powerplant is heated by the LP heater 32, deaerated by the deaerator 34, andthen turned to feedwater. Besides, a feedwater pipe 66 connecting thedeaerator 34 with the boiler 10 is installed in the feedwater system ofthe conventional thermal power plant. The feedwater in the conventionalthermal power plant is pressurized by the feedwater pump 36, heated bythe HP heater 37, and then returned to the boiler 10.

On the other hand, the feedwater in the gas turbine plant is led througha feedwater pipe 72 into the heat recovery steam generator 50, whichrecovers heat from the exhaust of the gas turbine 40, and turned tosteam by heat exchange with the gas turbine exhaust, and then joinedinto the main steam pipe 60 through the HP pipe 70 connecting the HPdrum 51 with the main steam pipe 60, and serves as superheated steam todrive the HP turbine 21.

Besides, the feedwater, having branched inside the heat recovery steamgenerator 50 and directed to the LP drum 52, is turned to steam by heatexchange with the gas turbine exhaust, and then joined into the hotreheat pipe 62 through the LP pipe 71 connecting the LP drum 52 with thehot reheat pipe 62, and serves as superheated steam to drive the IPturbine 22.

In normal operation, power generation cycle is repeated as above and theelectric energy is generated by the steam turbine generator 24, which isdriven by the directly-connected HP, IP and LP steam turbines 21, 22 and23, and also by the gas turbine generator 44, which is driven by thedirectly-connected gas turbine in this power plant.

While the plant continues operation in the above cycle under normalcondition, the conventional thermal power plant is equipped with asystem for dumping the generated steam into the condenser in case ofstart, stop and load rejection where the generated steam cannot bedirected into the steam turbine. In this embodiment, there is provided aturbine bypass system 1 that is branched from the main steam pipe 60 andconnected to the condenser 25 through the turbine bypass valve 8 andrelevant pipe. With this turbine bypass system 1, the steam generated bythe boiler 10 can be dumped into the condenser 25.

On the other hand, there is provided another turbine bypass system forthe steam generated by the heat recovery steam generator 50: a HRSG HPturbine bypass system 2 that is branched from the HP pipe 70 andconnected to the turbine bypass system 1 and a HRSG LP turbine bypasssystem 3 that is branched from the LP pipe 71 and connected to theturbine bypass system 1.

That is, in this embodiment, the HRSG high pressure turbine bypasssystem 2 (HRSG low pressure turbine bypass system 3) which is the secondturbine bypass system is connected in the middle of the first turbinebypass system 1. Furthermore, the turbine bypass system 1 from theconnecting point of the HRSG high pressure turbine bypass system 2 (HRSGlow pressure turbine bypass system 3) to a steam condenser 25 is sharedas a bypass system of the generating steam of the combustion boiler 10and the exhaust heat recovery boiler 50.

When building the parallel power generation system composed of the steampower generation plant, the gas turbine, and the exhaust heat recoveryboiler, by sharing a part of turbine bypass system 1 also as a turbinebypass system in the exhaust heat recovery boiler 50 such as thisembodiment, enlargement and complication of a steam condenser 25 isavoided, and it is able to reduce the cost of a steam condenser or aturbine bypass system considerably.

Moreover, when carrying out the re-powering by adding the gas turbineplant to an established steam power generation plant, largereconstruction of a steam condenser may be needed and it may not be ableto do in reconstruction depending on the case. However, it becomespossible to solve these problems by constituting a turbine bypass systemas mentioned above.

To start this power plant, the conventional thermal power plant isstarted first, and then the gas turbine plant is started. Accordingly,the boiler 10 is started first and the steam generated by the boiler 10is discharged into the condenser 25 through the turbine bypass system 1in the beginning, and then, when the pressure and temperature of thesteam generated by the boiler 10 become high enough to be supplied tothe steam turbine, the steam is led into the steam turbine.

Then, when the turbine bypass system 1 becomes not in operation or theamount of steam from the boiler 10 into the turbine bypass system 1becomes lower than a specified amount after the steam generated by theboiler 10 is all directed into the steam turbine, the gas turbine plantis started. The steam generated by the heat recovery steam generator 50is directed, through the HRSG HP turbine bypass system 2 and HRSG LPturbine bypass system 2, into the turbine bypass system 1 and thendischarged into the condenser 25.

When the pressure and temperature of the high-pressure steam from theheat recovery steam generator 50 become high enough to be mixed into themain steam, and when the pressure and temperature of the low-pressuresteam from the heat recovery steam generator 50 become high enough to bemixed into the hot reheat steam, each steam from the heat recovery steamgenerator 50 is mixed into the main steam pipe 60 and hot reheat pipe62, respectively, and the turbine bypass system 1 becomes not inoperation.

As the turbine bypass system 1 of the boiler 10 is put into service forthe boiler 10 and heat recovery steam generator 50 in turn as explainedabove, the turbine bypass systems 2 and 3 from the heat recovery steamgenerator can be connected each to the turbine bypass system 1 of theboiler 10.

The above operation is maintained so far as the control unit 80 monitorsthe opening state of the turbine bypass valve 8 and permits to start thegas turbine 40 only when the above operating condition is met.

In an event of load rejection or steam turbine tripping, generated steamcan no longer be directed into the steam turbine either in theconventional thermal power plant or in the gas turbine plant, and so thegenerated steam cannot be handled only by the turbine bypass system 1.Because of the above, it is recommended that each boiler pipe and HRSGpipe is equipped with a release valve 64 for releasing the steamgenerated in the conventional thermal power plant and gas turbine plantinto the air.

With the combined cycle plant according to this embodiment, because itis not necessary to install a system for dumping the generated steaminto the condenser in each conventional thermal power plant and gasturbine plant, the generated steam can be dumped into the condenserwithout increasing the number of inlet ports on the condenser of anexisting plant.

Besides, because the operating state of the gas turbine plant andconventional thermal power plant is monitored and each plant is startedin turn accordingly, it no longer happens that the steam generated inthe gas turbine plant and in the conventional thermal power plant isdumped into the condenser at the same time. Thus, the capacity of thedump system can decrease.

A typical embodiment of the present invention is as explained above.However, since there are different constructions available for thesystem for dumping the generated steam into the condenser, some more aredescribed hereunder.

<Embodiment 2>

FIG. 2 shows a preferred embodiment 2 of a combined cycle plantaccording to the present invention. The same devices and components asin FIG. 1 are denoted the same and no more explanation is given on them.Description hereunder covers differences only. In the figure, thecontrol unit 80 is not shown.

The plant is equipped with the turbine bypass system 1 as a system fordumping the generated steam into the condenser. The turbine bypasssystem of this embodiment is branched from the main steam pipe 60 at theoutlet of the primary superheater 14, directed through the pipe and theflash tank 4, and then piped and connected to the condenser 25. Withthis turbine bypass system 1, the steam generated at the start of theboiler 10 is dumped into the condenser 25.

The plant is also equipped with another turbine bypass system fordumping the steam generated by the heat recovery steam generator 50: theHRSG HP turbine bypass system 2 that is branched from the HP pipe 70 andconnected to the flash tank 4, and the HRSG LP turbine bypass system 3that is branched form the LP pipe 71 and connected to the flash tank 4.The point of connection of each turbine bypass system from the heatrecovery steam generator 50 can be located not only on the flash tank 4but also on the pipe near the flash tank 4.

<Embodiment 3>

FIG. 3 shows a preferred embodiment 3 of a combined cycle plantaccording to the present invention. The same devices and components asin FIG. 1 and FIG. 2 are denoted the same and no more explanation isgiven on them. Description hereunder covers differences only. In thefigure, the control unit 80 is not shown.

As the turbine bypass system for the boiler 10, the plant is equippedwith the HP turbine bypass system 1 a that is branched from the mainsteam pipe 60 and connected to the cold reheat pipe 61 and the LPturbine bypass system 1 b that is branched from the hot reheat pipe 62and connected to the condenser 25. Besides, a main steam pipe drainsystem 5 connecting the main steam pipe 60 with the condenser 25 is alsoinstalled. The main steam pipe drain system 5 and LP turbine bypasssystem 1 b serve as a system for dumping the generated steam into thecondenser.

The HRSG HP turbine bypass system 2 is connected to the main steam pipedrain system 5 and the HRSG LP turbine bypass system 3 is connected tothe LP turbine bypass system 1 b so as to serve as the turbine bypasssystem for the steam generated by the heat recovery steam generator.

<Embodiment 4>

FIG. 4 shows a preferred embodiment 4 of a combined cycle plantaccording to the present invention. The same devices and components asin FIGS. 1 to 3 are denoted the same and no more explanation is given onthem. Description hereunder covers differences only. In the Figure, thecontrol unit 80 is not shown.

The plant of this embodiment is equipped with the secondary superheaterbypass system 6 connecting the main steam pipe 60 with the condenser 25.The secondary superheater bypass system 6 and LP turbine bypass system 1b are installed to serve as the system for dumping the generated steaminto the condenser.

The HRSG HP turbine bypass system 2, branched from the HP pipe 70 andconnected to the secondary superheater bypass system 6, and HRSG LPturbine bypass system 3, branched from the LP pipe 71 and connected tothe LP turbine bypass system 1 b, are installed to serve as the turbinebypass system for the steam generated by the heat recovery steamgenerator 50.

<Embodiment 5>

FIG. 5 shows a preferred embodiment 5 of a combined cycle plantaccording to the present invention. The same devices and components asin FIGS. 1 to 4 are denoted the same and no more explanation is given onthem. Description hereunder covers differences only. In the Figure, thecontrol unit 80 is not shown.

The plant of this embodiment is equipped with the superheater inlet dumpsystem 7 connecting the main steam pipe 60 with the condenser 25. Thesuperheater inlet dump system 7 and turbine bypass system 1 serve as thesystem for dumping the generated steam into the condenser.

The HRSG HP turbine bypass system 2, branched from the HP pipe 70 andconnected to the turbine bypass system 1, and HRSG LP turbine bypasssystem 3, branched from the LP pipe 71 and connected to the superheaterinlet dump system 7, are installed to serve as the turbine bypass systemfor the steam generated by the heat recovery steam generator 50.

<Embodiment 6>

FIG. 6 shows a preferred embodiment 6 of a combined cycle plantaccording to the present invention. The same devices and components asin FIGS. 1 to 5 are denoted the same and no more explanation is given onthem. Description hereunder covers differences only. In the figure, thecontrol unit 80 is not shown.

In the plant of this embodiment, an attemperator 9 is installed on theturbine bypass system 1, and both HRSG HP turbine bypass system 2 andHRSG LP turbine bypass system 3 are connected to the turbine bypasssystem 1. The point of connection is located on a pipe from the turbinebypass valve 8 to the attemperator 9.

Assuming that a combined cycle plant is to be constructed, there may beseveral different cases available in addition to a case where a newcombined cycle plant is constructed from the scratch as above: forexample, a case where a gas turbine plant is newly added to the existingconventional thermal power plant or a case where boiler and gas turbineplant are newly installed but the existing steam turbine is put intouse.

When a new power plant according to the present invention is to beconstructed, installing respective dump systems for dumping the steamgenerated in the conventional thermal power plant and gas turbine plantinto the condenser is not necessary. Even in the case where a gasturbine plant is to be added to an existing conventional thermal powerplant, no additional inlet port needs to be installed on the condenserto receive a dump system for the steam generated by the heat recoverysteam generator, and so large-scale remodeling of the condenser is notneeded.

The meaning of Reference signs in Figs. are as follows:

1 . . . Turbine bypass system, 2 . . . High pressure turbine bypasssystem of HRSG, 3 . . . Low pressure turbine bypass system of HRSG, 4 .. . Flash tank, 5 . . . Drain system of main steam pipe, 6 . . . Bypasssystem of secondary superheater, 7 . . . Dump system at superheaterinlet, 8 . . . Turbine bypass valve, 9 . . . Attemperator, 10 . . .Boiler, 11 . . . Reheater, 12 . . . Economizer, 13 . . . Evaporator, 14. . . Primary superheater, 15 . . . secondary superheater, 21 . . . HP(high-pressure) turbine, 22 . . . IP (intermediate-pressure) turbine, 23. . . LP (low-pressure) turbine, 24 . . . Steam turbine generator, 25 .. . Condenser, 30 . . . Condensate pump, 31 . . . Gland steam condenser,32 . . . LP (low-pressure) heater, 34 . . . Deaerator, 36 Feedwaterpump, 37 . . . HP (high-pressure) heater, 40 . . . Gas turbine, 41 . . .Compressor, 42 . . . Turbine, 43 . . . Combustor, 44 . . . Gas turbinegenerator, 50 . . . Heat recovery steam generator, 51 . . . HP drum, 52. . . LP drum, 60 . . . Main steam pipe, 61 . . . Cold reheat pipe, 62 .. . Hot reheat pipe, 63 . . . Crossover pipe, 64 . . . Release valve, 70. . . HP pipe, 71 . . . LP pipe, 72 . . . Feedwater pipe, 80 . . .Control unit.

According to the present invention, because installing respective dumpsystems for dumping the steam generated in the conventional thermalpower plant and gas turbine plant into the condenser is not necessary, asystem for dumping the generated steam into the condenser can beconstructed without increasing the number of inlet ports on thecondenser of an existing plant.

1. A combined cycle plant equipped with a conventional thermal powerplant having a boiler, boiler pipe including main steam pipe, coldreheat pipe and hot reheat pipe, steam turbine; condenser; andcondensate water/feedwater system, and a gas turbine plant having a gasturbine, heat recovery steam generator recovering heat from the gasturbine exhaust, and heat recovery steam generator pipe supplying thegenerated steam from the heat recovery steam generator to the steamturbine, the combined cycle plant further comprising: a dump systemconnecting the boiler pipe with the condenser and dumps the steamgenerated by the boiler into the condenser, bypassing the steam turbine;and a pipe connecting the heat recovery steam generator pipe with thedump system into the condenser, wherein the dump system into thecondenser is a turbine bypass system equipped with a flash tank and thepoint of connection between the heat recovery steam generator and thedump system into the condenser is located on the flash tank of theturbine bypass system or on a pipe near the flash tank.
 2. A combinedcycle plant equipped with a conventional thermal power plant having aboiler, boiler pipe including main steam pipe, cold reheat pipe and hotreheat pipe, steam turbine; condenser; and condensate water/feedwatersystem, and a gas turbine plant having a gas turbine, heat recoverysteam generator recovering heat from the gas turbine exhaust, and heatrecovery steam generator pipe supplying the generated steam from theheat recovery steam generator to the steam turbine, the combined cycleplant further comprising: a dump system connecting the boiler pipe withthe condenser and dumps the steam generated by the boiler into thecondenser, bypassing the steam turbine; and a pipe connecting the heatrecovery steam generator pipe with the dump system into the condenser,wherein the dump system into the condenser is equipped with a turbinebypass valve and attemperator and the point of connection between theheat recovery steam generator and the dump system into the condenser islocated on a pipe between the turbine bypass valve and the attemperator.3. A combined cycle plant equipped with a conventional thermal powerplant having a boiler, boiler pipe including main steam pipe, coldreheat pipe and hot reheat pipe, steam turbine; condenser; andcondensate water/feedwater system, and a gas turbine plant having a gasturbine, heat recovery steam generator recovering heat from the gasturbine exhaust, and heat recovery steam generator pipe supplying thegenerated steam from the heat recovery steam generator to the steamturbine, the combined cycle plant further comprising: a dump systemconnecting the boiler pipe with the condenser and dumps the steamgenerated by the boiler into the condenser, bypassing the steam turbine;a pipe connecting the heat recovery steam generator pipe with the dumpsystem into the condenser and a valve that is installed in the dumpsystem into the condenser and a control unit that employs statevariables of the valve as input and controls the start timing of the gasturbine plant.
 4. A combined cycle power plant including a combustionboiler, a steam turbine driven by the steam generated by the combustionboiler, and a combustion boiler steam pipe supplying the steam generatedby the combustion boiler to said steam turbine, a condenser whichcondenses the steam discharged from the steam turbine, and including agas turbine plant having a gas turbine, a exhaust heat recovery boilerwhich uses the gas turbine as a heat source and a exhaust heat recoveryboiler steam pipe which supplies the steam generated bys aid exhaustheat recovery boiler to the combustion boiler steam pipe, the combinedcycle power plant further comprising: a first turbine bypass systemwhich bypasses the steam of the combustion boiler steam flowing throughthe combustion boiler steam pipe; a second turbine bypass system whichbypasses the steam of the exhaust heat recovery boiler supplied to thesteam turbine through the combustion boiler steam pipe and flown throughthe combustion boiler steam pipe; wherein the first and second bypasssystems are shared partially and the generated steam of the combustionboiler and/or the exhaust-heat recovery boiler are dumped to thecondenser through the shared first and second bypass systems.